Liberal Democrat leader Nick Clegg has called on his party to "hold your nerve" as he prepared to face activists unsettled by plummeting poll ratings and by-election disaster.

In an interview on the eve of the party's spring conference in Sheffield, the Deputy Prime Minister insisted he believes he was right to take the Lib Dems into coalition with Conservatives and right in the agenda the Government has followed.

Conference opens against the humiliating backdrop of sixth place in last week's Barnsley Central by-election, with many rank-and-file members unhappy about Mr Clegg's U-turns on issues like university tuition fees and the pace of spending cuts.

The latest YouGov survey for The Sun put the Lib Dems on just 9%, trailing well behind their Conservative coalition partners on 34% and Labour on 45%. Labour's 11-point lead is the largest the company has recorded since the election.

But Mr Clegg will seek to win followers over with a list of achievements which he will say are down to the Lib Dem presence in Government, from restored civil liberties and the pupil premium in schools to the referendum on electoral reform, the banking levy and measures to take thousands of low-income households out of income tax.

The party is going through a "difficult time" but by the time of the general election, the Government will have "wiped the slate clean" of the deficit and voters will be ready to judge it more kindly, he said.

Speaking to The Independent, Mr Clegg signalled that he was ready to strike a more independent tone by disagreeing publicly with David Cameron. And he even revealed that he told the Prime Minister he was talking "complete bilge" when Mr Cameron defended the first-past-the-post system in the House of Commons on Wednesday.

Insisting that he will not be blown off course by polling setbacks, Mr Clegg said: "We are in this for the long haul. We are going to keep our nerves. We are not going to flinch. We were right to go into government. We are doing the right things in government."

"We should never forget what are are in politics for," he said. "Without the Liberal Democrats, you would not have got a huge restoration of civil liberties; a balanced approach to Europe; a ferocious protection of human rights; a very heavy emphasis on more resources to our schools; the pupil premium; lifting thousands and thousands of people out of income tax; a £10 billion levy on the banks; a crackdown on tax loopholes, a referendum in May on the voting system.

"These are early days - 10 months into a five-year Parliament. All the focus is on the immediate task of the deficit. People have to hold their nerve, not lurch from one thing to the next. You have to work at it day in, day out and deliver over time, so that people see the difference you make. That is what we do and we will continue to do."